The development of techniques for the isolation and in vitro culture of multipotent neural stem cells (for example, see U.S. Pat. Nos. 5,750,376; 5,980,885; 5,851,832) significantly improved the outlook for the treatment of neurodegenerative diseases and conditions. It was discovered that fetal brains can be used to isolate and culture multipotent neural stem cells in vitro. Moreover, in contrast to the long held belief that adult brain cells are not capable of replicating or regenerating brain cells, it was found that neural stem cells may also be isolated from brains of adult mammals. These stem cells, either from fetal or adult brains, are capable of self-replicating. The progeny cells can proliferate or differentiate into any cell in the neural cell lineage, including neurons, astrocytes and oligodendrocytes. Therefore, these findings not only provide a source of neural cells which can be used in transplantations but also demonstrate the presence of multipotent neural stem cells in adult brain.
Certain agents, neural stem cell proliferating agents, have been found to increase the number of neural stein cells in vitro or in vivo. The mechanisms for such increase may include stimulating proliferation, inhibiting differentiation, and/or preventing death of the neural stem cells. Additional agents, stem cell differentiating agents, have been found to selectively enhance the production of neuronal precursor cells or glial precursor cells in vitro or in vivo. These proliferating and differentiating agents can thus be employed to increase and selectively enhance neurons and glial cells.